On 11 April 2023, the planet Mercury will be at greatest elongation, which is the best time to look for it in the night sky. Since Mercury is the innermost planet of the solar system, it usually appears close to the sun in the sky, making it tricky to spot – so grab this opportunity while you can.
What is greatest elongation?
Greatest elongation means the planet is at its furthest distance from the sun as viewed from Earth. For Mercury, this means there is a chance to spot it, but you will still have to be quick. It will be easier to see in the northern hemisphere because this half of Earth is currently angled towards the sun, meaning Mercury will appear higher above the horizon than it will in the southern hemisphere.
How do I see Mercury?
Look towards the western horizon as soon as the sun has set. It might still be quite light outside, but you should be able to make out the glow of Mercury with the naked eye. Binoculars will give you a better view.
Why is it so difficult to see Mercury?
Mercury, like Venus, is called an inferior planet because it orbits closer to the sun than Earth does. Seeing these planets depends on them being as far from the sun as possible because, when they are right next to it, the light they reflect is outshone by the sun itself. This matters more for Mercury than it does for Venus because Mercury is closer to the sun, not to mention much smaller and fainter than Venus.
Just how small is Mercury?
The rocky planet, which has a cratered surface rather like our moon’s, is less than 5000 kilometres in diameter. That makes it smaller than Jupiter’s moon Ganymede, which is much easier to observe – just point a pair of binoculars at Jupiter and you should be able to see it, along with Jupiter’s other large moons Io, Europa and Callisto.